In human patients with asthma and airway inflammation, levels of NITRIC OXIDE (NO) in both expired air and tracheobronchial epithelial cells are increased, as is mucin secretion. We propose that NO generated within these airway epithelial cells is a KEY INTRACELLULAR SIGNALLING MOLECULE playing a central role affecting mucin hypersecretion associated with airway inflammation and disease. The concept behind this proposal is that diverse stimuli act to increase secretion of airway mucin via a convergent pathway involving intracellular production of NO as the critical signalling molecule. The specific hypothesis to be addressed is that NO is involved in provoking mucin hypersecretion in airway epithelial cells via the following mechanism: NO produced by the catalytic action of the enzyme, nitric oxide synthase (NOS) increases intracellular levels of cyclic GMP (cGMP). cGMP, via activation of cGMP associated protein kinases (PKG's) provokes release of mucin granules. It is proposed that this mechanism is involved in the hypersecretory response to specific stimuli associated with airway inflammation and disease. However, the intracellular mechanisms that lead to production of NO by these hypersecretory stimuli operate via separate and independent second messenger pathways. Our preliminary data indicate that there exist at least three separate signal transduction pathways that can be activated by diverse stimuli and converge to produce NO as the key which triggers release of mucin granules. The experiments proposed will elucidate these second messenger pathways leading to NO production and resultant mucin hypersecretion activated by three selected, directly relevant mediators known to be associated with asthma and/or airway inflammation: l. HISTAMINE: 2. TUMOR NECROSIS FACTOR alpha; and 3. REACTIVE OXYGEN SPECIES. The experiments in this proposal will determine if the above-NO dependent mechanism modulates mucin secretion in GUINEA PIG TRACHEAL EPITHELIAL CELLS, maintained in an air/liquid interface primary culture, a system developed in this laboratory that maintains airway epithelial cells with differentiated structure and function. These studies will demonstrate the existence of a convergent pathophysiological pathway modulating a primary respiratory defense mechanism, mucin secretion.